/**
 * 基于BST实现的映射
 *
 * @author Kevin
 * @date 2018-12-15
 */
public class BSTMap<K extends Comparable<K>, V> implements Map<K, V> {

    /**
     * 根节点
     */
    private Node root;

    /**
     * 大小
     */
    private int size;

    public BSTMap() {
        this.root = null;
        this.size = 0;
    }

    @Override
    public void add(K key, V value) {
        this.root = add(this.root, key, value);
    }

    @Override
    public V remove(K key) {
        Node node = getNode(this.root, key);
        if (node != null) {
            this.root = remove(this.root, key);
            return node.value;
        }
        return null;
    }

    @Override
    public boolean contains(K key) {
        return getNode(root, key) != null;
    }

    @Override
    public V get(K key) {
        Node node = getNode(this.root, key);
        return node == null ? null : node.value;
    }

    @Override
    public void set(K key, V newValue) {
        Node node = getNode(this.root, key);
        if (node == null) {
            throw new IllegalArgumentException(key + " doesn't exist!");
        }

        node.value = newValue;
    }

    @Override
    public int getSize() {
        return this.size;
    }

    @Override
    public boolean isEmpty() {
        return this.size == 0;
    }

    /**
     * 向以node为根的二分搜索树中插入元素(key,value)，返回插入新节点后二分搜索树的根
     *
     * @param node
     * @param key
     * @param value
     * @return
     */
    private Node add(Node node, K key, V value) {
        if (node == null) {
            this.size++;
            return new Node(key, value);
        }

        if (key.compareTo(node.key) < 0) {
            node.left = add(node.left, key, value);
        } else if (key.compareTo(node.key) > 0) {
            node.right = add(node.right, key, value);
        } else {
            node.value = value;
        }

        return node;
    }

    /**
     * 返回以node为根节点的二分搜索树中key所在的节点
     *
     * @param node
     * @param key
     * @return
     */
    private Node getNode(Node node, K key) {
        if (node == null) {
            return null;
        }

        if (key.equals(node.key)) {
            return node;
        } else if (key.compareTo(node.key) < 0) {
            return getNode(node.left, key);
        } else {
            return getNode(node.right, key);
        }
    }

    /**
     * 返回以node为根的二分搜索树的最小值所在的节点
     *
     * @param node
     * @return
     */
    private Node minimun(Node node) {
        if (node.left == null) {
            return node;
        }

        return minimun(node.left);
    }

    /**
     * 删除掉以node为根的二分搜索树中的最小节点，返回删除节点后的新的二分搜索树的根
     *
     * @param node
     * @return
     */
    private Node removeMin(Node node) {
        if (node.left == null) {
            Node rightNode = node.right;
            node.right = null;
            this.size--;
            return rightNode;
        }

        node.left = removeMin(node.left);
        return node;
    }

    /**
     * 删除掉以node为根的二分搜索树中键为key的节点
     *
     * @param node
     * @param key
     * @return
     */
    private Node remove(Node node, K key) {
        if (node == null) {
            return null;
        }

        if (key.compareTo(node.key) < 0) {
            node.left = remove(node.left, key);
            return node;
        } else if (key.compareTo(node.key) > 0) {
            node.right = remove(node.right, key);
            return node;
        } else {
            // 待删除节点左子树为空的情况
            if (node.left == null) {
                Node rightNode = node.right;
                node.right = null;
                this.size--;
                return rightNode;
            }

            // 待删除节点右子树为空的情况
            if (node.right == null) {
                Node leftNode = node.left;
                node.left = null;
                this.size--;
                return leftNode;
            }

            // 待删除节点左右子树均不为空的情况
            // 找到比待删除节点大的最小节点，即待删除节点右子树的最小节点
            // 用这个节点顶替待删除节点的位置
            Node successor = minimun(node.right);
            successor.right = removeMin(node.right);
            successor.left = node.left;

            node.left = node.right = null;

            return successor;
        }

    }

    /**
     * 节点类
     */
    private class Node {
        public K key;
        public V value;
        public Node left, right;

        public Node(K key, V value) {
            this.key = key;
            this.value = value;
            this.left = null;
            this.right = null;
        }
    }

}
